This invention relates generally to the field of communications, and more specifically to the processing of analog speech signals to extract pitch information therefrom.
The problem of deriving pitch information from a speech signal occurs in nearly all aspects of speech processing, particularly in the vocoder or linear predictive coding area, where one must, after deriving a instantaneous model of the vocal tract, provide a suitable excitation, or fundamental tone, to that model in order to reconstruct the speech. Devices have been developed over the past several years to accomplish this purpose, but all have disadvantages which are solved by this invention. Devices which analyze a signal by first stepping the signal into a shift register tapped at regular intervals have significantly reduced accuracy as the pitch period decreases, and they require significantly increased processing time because of unnecessary accuracy at longer pitch periods. Other devices have attempted to derive pitch by locating regularly-occurring peaks in the speech signal. These devices are ineffective if the signal contains significant amounts of noise. Many pitch tracking processes either require extensive amounts of logic and computation (such as Fourier transforms) or require several passes through the speech signal, thereby prohibiting implementation in real time. It would be desirable to have a process for extracting pitch information which would overcome these disadvantages, and it is to this end that this invention is directed.